The present invention relates generally to the field of oil and gas well cementing. More particularly, the present invention relates to an instrumented cementing plug and a system for sending to a surface location data measured by the instrumentation of the cementing plug.
During the drilling and at the completion of every oil and gas drilling operation, it is necessary that cementing be done in the borehole. More particularly, the casing or liner must be cemented in the hole in order to support the casing or liner and the hole and to prevent the flow of fluids between formations.
The operations associated with setting and cementing casing and liners in the borehole are generally well known in the art. At the completion of a phase of drilling, the cased and open portions of the well bore are filled with drilling fluid. A casing or liner string is assembled and run into the well bore. Then, a spacer or displacement plug is inserted into the top of the casing or liner above the drilling fluid. The displacement plug serves to separate and prevent mixing of the drilling fluid below the displacement plug and a cement slurry that is pumped into the casing or liner above the displacement plug. After a predetermined quantity of cement slurry has been pumped into the casing or liner, a cementing plug is inserted above the cement slurry. Then, drilling fluid is pumped into the casing above the cementing plug to force the slug of cement slurry down the casing or liner and up the annulus between the casing or liner and the borehole. After cementing, the displacement and cementing plugs, the cementing shoe, and any residual cement in the casing are drilled out.
Good cementing jobs are essential to the successful drilling and completion of oil and gas wells. Currently, operators rely upon proper equipment and skill of personnel in order to achieve a good cementing job. However, occasionally, bad cementing jobs occur. Some of the causes of bad cementing jobs are over-displacement or under-displacement of the cement slurry, which results in the formations not be properly isolated from each other. Another cause of bad cementing jobs channeling within the cement, which results in flow paths within the cement between formations.
Various tests are performed to determine whether or not the cementing job is good. If a cementing job is not good, then remedial operations, such as squeeze jobs, must be undertaken. However, remedial operations, tend to be expensive in terms of equipment and supplies and time.
It is an object of the present invention to provide a system for improving the quality of cementing operations.
The present invention provides a system for cementing a tubular member, such as a casing or liner string, in a well bore. The system of the present invention includes a cementing plug. The cementing plug includes at least one sensor. The system transmits a value measured by the sensor to a surface location. The system may transmit the value measured by the sensor through a cable connected between the plug and the surface location. Alternatively, the system may transmit the value measured by the sensor in a wireless manner to the surface location. In a cable-connected embodiment, an optical transmitter may be coupled to the sensor and the cable may include an optical fiber. In a wireless embodiment, the signal may be acoustically coupled to the surface. For example, an explosive device for producing an acoustic signal may be coupled to the sensor.